The influenza vaccine has been updated annually for decades to chase viral evolution, and some influenza viruses show no sign of slowing down. While transmissibility of viruses does plateau at a certain point, other human viruses that escape immunity keep doing so. It’s impossible to say whether future variants will have more big Omicron-like jumps or more typical stepwise changes, but we are confident SARS-CoV-2 will continue to evolve to escape immunity. It’s not known exactly how the virus made the big evolutionary jump that led to Omicron, although many scientists (including us) suspect the variant may have emerged from someone who couldn’t fight off the virus well, allowing it time to mutate. But evolution defied our expectations, and we got Omicron, which has a huge number of mutations and isn’t descended from Delta. That’s why six months ago many scientists, including us, thought the next variant would descend from Delta, which was dominant at the time. Evolution often proceeds stepwise, with new successful variants descended from recent successful ones. The fact that the virus developed the ability to infect people who had been vaccinated or previously infected shouldn’t have been a surprise, but how it happened with Omicron certainly was. This, coupled with how contagious Omicron is, has enabled it to cause a huge wave of infections. Prior variants like Delta were only modestly able to sidestep antibodies, but Omicron has many mutations that reduce the ability of antibodies to recognize it. The importance of immune escape has become apparent with Omicron. Because these antibodies can block infection, variants with mutations that skirt them have an increasing advantage. But now much of the world has antibodies from vaccination or prior infection. Early in the pandemic, few people had immunity to SARS-CoV-2. Viruses such as this one can also spread better by “escaping” immunity to prior variants. We don’t know when this coronavirus will hit its transmissibility plateau, but it will happen eventually. Others, such as influenza, are generally not as contagious as SARS-CoV-2. Some respiratory viruses such as measles are more contagious than today’s SARS-CoV-2. Other viruses have reached plateaus in their ability to spread. Even evolution is constrained: a cheetah can’t evolve to be infinitely fast, and SARS-CoV-2 won’t become infinitely transmissible. How much more transmissible SARS-CoV-2 can become is an open question, but there are limits. Figures for Omicron reflect the variant’s BA.1 lineage and are extrapolated based on findings of a 105 percent growth advantage by Omicron compared with Delta. Antibody escape is based on antibody sera collected from patients treated with the Moderna vaccine. Sources: Contagiousness is based on estimates of growth advantage by Marlin Figgins and Trevor Bedford. These big jumps in contagiousness have played a major role in driving the pandemic so far. That’s a huge increase, and makes SARS-CoV-2 more contagious than many other human respiratory viruses. Recent variants like Omicron and Delta are several times more transmissible than the strain that first spread around the globe in early 2020. This coronavirus has undergone several adaptations that make it better at spreading in humans.īut although many scientists, including us, expected SARS-CoV-2 would be under evolutionary pressure to transmit better, it’s been remarkable just how well the virus has responded to that pressure. The virus can do this by becoming more contagious and by skirting the immune system. Viruses that cause more infections will be more successful. Note: Figures for Omicron mutations show only the mutations present in the BA.1 lineage.Ī virus like SARS-CoV-2 faces one overriding pressure: to become better at spreading. Source: Bloom Lab (Fred Hutchinson Cancer Research Center) research and analysis of GISAID viral genetic sequence data.
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